Amplifying circuit arrangement for ultra high frequencies



Jan. 13, 1948. M. J. o. STRUTT ETAL 2,434,295 AMPLIFYING CIRCUIT ARRANGEMENT FOR ULTRA HIGHQFREQUENCIES Filed March 23, 1943 6 751177 4L DEBT VA/V .DEB Z/EL Patented Jan. 13, 1948 2,434.295 l C E AMPLIFYIN G CIRCUIT ARRANGEMENT FOR ULTRA HIGH FREQUENCIES Maximiliaan Julius Otto Strutt and Aldert van der Ziel, Eindhoven, Netherlands, assignors to Hartford National Bank and Trust Company, Hartford, Conn., as trustee Application March 23, 1943, Serial No. 480,194 In the Netherlands May 30, 1940 9 Claims.

This invention relates to an electron discharge device and its associated amplifying circuit arrangement for use at ultra-high frequencies in which use is made of an amplifying tube having such a size and operating voltage that the transit time of the electrons is greater than the period of the oscillations to be amplified.

At ultra-high frequencies the properties of amplifying tubes are very difierent from those at lower frequencies. Particularly in amplifying ultra-high frequencies the fact must be taken into account that a virtual ohmic resistance having a comparatively low value is set up between the control grid and the cathode, which resistance exerts a strong damping on the input circuit. The presence of this virtual ohmic resistanc is mainly due to two causes.

Primarily a phase displacement will occur between the alternating control grid voltage and the electronic stream passing through the apertures of the control grid, which phase displacement is due to the comparatively long transit time of the electrons and involves the appearance of an influencing current to the control grid. This influencing current has a component which is in phase with the alternating control grid voltage and may be conceived to be caused by a. virtual ohmic resistance set up between the control grid and the cathode. The reciprocal value of this resistance is called transit time damping or electron damping.

Secondly the natural inductances of the supply leads to the various electrodes will exhibit a considerable impedance to the oscillations to be amplified so that high frequency voltages ar set up across these supply leads which voltages rise to currents through the natural tube capacities. Across the inductance of the cathode lead, for instance, a voltage will be set up which leads in phase by 90 with respect to the alternating control grid voltage and produces a current from the control grid to the cathode through the control grid cathode capacity, which current is in phase with th alternating control grid voltage. Similar current will also flow from th control grid through the tube capacities to other electrodes. The damping of the input circuit thus produced may be called lead damping.

Between anode and cathode there is also set up a virtual ohmic resistance whose reciprocal value is called output damping and which is substantially caused under the influence of the impedances of the supply leads for the electrodes in cooperation with the tube capacities. Consequently the output damping may be conceived to be lead damping; as a rule it is much smaller than the input damping.

Both the electron damping and the lead damping are substantially proportional to the square of the frequency of the oscillations to be amplified. At ultra high frequencies the input damping resulting from these two components is generally so high that the impedance of the oscillaable amplification per stage substantially corv responds to the product of mutual conductance and input resistance. Hence, in order to obtain sufiicient amplification at ultra high frequencies the attempts are to be directed to an input resistance which is as high as possible. At wavelengths of a few meters the usual high frequency amplifying tubes exhibit such a small input resistance that amplification is practically no longer possible. Therefore very small tubes have hitherto mainly been used for amplifying very high frequencies, in which as a result of their very small size both the transit time of the electrons and the impedances of the supply leads are reduced to a minimum so that the input damping is slight. However, these small tubes exhibit the drawback that due to their small size the mutual conductance is also very low and generally does not exceed about 1.5 ma./v. The product of mutual conductance and input resistance is comparatively small also with these tubes so that amplification is no longer obtainable at wavelengths below about 60 cms.

Recently various proposals have been made to reduce the input damping of amplifying tubes. The lead damping, for instance, can be reduced by making use of a tube having two cathode supply leads, one of which is included in the input circuit nd the other in the output circuit. Another expedient to reduce the lead damping consists in the use of amplifying tubes comprising two push-pull connected amplifying systems of which the cathodes ar connected through as short a lead as possible. This last mentioned expedient also yields a decrease in output damping.

Another improvement of the input damping is possible by taking various measures which in principle amount to back coupling, for instance by the interposition of a supplementary inductance in the screen grid lead or, in secondary emission tubes, by connecting the secondary emission electrode to the control grid and to the cathode through suitable impedances.

Again a very suitable method of reducing the input damping consists in the artificial increase of the inductance of the cathode supply lead or the screen grid control grid capacity interposed in the output circuit of a tube having two cathode supply leads. In secondary emission tubes this eifect can still be increased by leading the second- 3 ary emission current through the cathode supply lead interposed in the input circuit and by increasing artificially the inductance of this cathode supply lead or the control grid cathode capacity or both. 7

In order that the above measures for decreasing the input damping may be efiective it is always necessary, however, that the tubehas a comparatively high mutual conductance, so that in small tubes no particular results are to be expected from these measures.

To ensure a high mutual conductance the tube must generally be given a fairly large size. Furthermore, a suitable expedient for increasing the mutual conductance consists in the use of one or more stages of secondary emission, but in this case it is necessary, for electro-optical reasons, that the distance between two succeeding secondary emission electrodes and between the last secondary emission electrode and the anode respectively at least amounts to about 1.5 cm. Therefore an increase in mutual conductance generally involves such distances between the various electrodes that at ultra high frequencies the transit time of the electrons is greater than the period of the oscillations to be amplified.

Upon using such tubes with comparatively large distances between the electrodes the difiiculty arises that the effective mutual conductance which occurs in amplifying ultra high frequencies is much smaller than the static mutual conductance, so that the requisite greater mutual conductance is not attained in practice.

The invention has for its object the'provision of a tube and circuit for overcoming the above difilculties.

For this purpose the ends of the output impedance are, according to the invention, connected respectively to two electrodes which are located in the path of the electrons and whose mutual distance is covered by the electrons in less than half a period of the oscillations to be amplified.

The novel features which We believe to be characteristic of our invention are set forth with particularity in the app nded claims, but the invention itself will best be understood by reference to the following description taken in connection with the accompanying drawing in which Figures 1 and 2 are circuit diagrams explaining the operation of tubes and how our invention applies to the same, Figures 3 and 4 are schematic diagrams illustrating the principles involved in an electron discharge device made according to our invention, Figure 5 is a characteristic diagram illustrating the principles involved in our invention, Figures 6 and 7 are schematic diagrams of an electron discharge device and associated circuits made according to our invention.

The invention is based on the following recognitions:

The phenomenon that in ampliiying ultra high frequencies the eiiective mutual conductance is smaller than the static mutual conductance cannot be accounted for when starting from the customary view, viz. that the electrons first flow from the cathode to the anode and then return to the cathode through the output impedance, In fact, even at ultra high frequencies the alternating voltage acting at the control grid divides the electronic stream in succeeding concentrations and deconcentrations of electrons all of which reach the anode, although with a certain time lag. In conformity with this view, one may suppose that all of the said concentrations and deconcentrations will also pass through the output imped 4, ance,'sothat the mutualconductance would have to be independent of the transit time of the electrons.

In reality, however, the current does not flow first through the tube and then through the output impedance, but the currents inside and outside the tube iiow atthe same time, as will be the-anode voltage on the cathode current may be neglected. In this figure a triode is provided with an envelope I containing a cathode 2, a control grid 3 and an anode 4. The control grid circuit includes an input impedance 5, and the anode circuit comprises an output impedance 6. For the sake of simplicity the supplies have been omitted.

Upon abrupt application of a positive voltage to the control grid 3 of the triode a number of electrons will at the same time leave the cathode 2. These electrons leave a positive image charge in the cathode. At the'beginning these electrons travel slowly and then at an ever-increasing speed in the direction of the control grid, the positive image charge prevailing in the cathode decreasing gradually, At the same time an increasing positive image charge is produced in the control grid and at the moment in which the electrons attain the plane of the control grid a positive image charge corresponding to their charge is accumulated in :the control grid, whereas the image charge in the cathode has substantially entirely disappeared. During the time the electrons have traveled from the cathode to the control grid a displacement of a positive charge from the cathode to the control grid has taken place at the-same:time; i. e. a current has flown in the external circuit between cathode and control grid. If the electrons staying in the plane of the control grid were intercepted by the control grid (grid current) they would be neutralized by the positive image charge accumulated in the control grid and the whole phenomenon would be ended.

When the said electrons are passed by the control grid the image charge accumulated in the control grid gradually decreases and at the same time an image charge is produced in the anode 4. When the electrons attain the anode a positive image charge corresponding to their charge has already been accumulated in the anode and in the meantime the image charge in the control grid has disappeared. The electrons are now intercepted'by the anode and neutralized by the positive charge accumulated therein and the event has ended. During the time in which the electrons travel from the control grid to the anode-a charge displacement has taken place through the external circuit of the control grid to the anode, in other terms a current has passed in the anode circuit during the time in which the electrons travel within the tube from the control grid to the anode.

Consequently, during the travel of the electrons from the cathode to the anode there first flows a current Ik from the cathode to the control grid and then a current Ia flows from the control grid to the anode.

Similarly in a tetrode a current Ir will first flow from the cathode to the control grid, a current Is will flow from the control grid to the screen grid and finally a current IE. will flow from the screen grid to the anode, These currents are inic in He 2 represe tin a 1 613. 1 havin a cathode 2, a control grid 3, a screen grid 1 and an anode 4. In this case the anode current is exclusively produced by the charge displacement through the external circuit of the screen grid 1 to the anode 4 during the time in which the electrons travel within the tube from the screen grid to the anode.

From the above considerations it appears that the anode current is exclusively determined by the displacement of the electrons in the space between the anode and the preceding electrode. It will be obvious that the anode current is larger as there are more electrons between these two electrodes and as these electrons travel more rapidly. On the other hand the anode current is smaller as the distance from the anode to the preceding electrode is larger. The anode current may at least approximately be expressed by the formula:

0 a NpE I in which p represents the charge of an electron,

v the speed of an electron in question and a the distance between the anode and the preceding electrode, the index N indicating that the summation must be extended to all electrons in the space between the anode and the preceding electrode. If the anode and the preceding electrode have the same potential, so that the speed of the electrons between the said two electron is constant, we have the expression In order that the value of the alternating anode current can be fixed, the influence of the electrons in the space between the anode and the preceding electrode must be more fully considered. The alternating voltage acting at, the control grid divides the electronic stream in succeeding concentrations and deconcentrations; during the positive half cycle of the alternating control grid voltage the number of electrons emitted by the cathode is larger than is normally the case so that concentration occurs, whereas during the negative half cycle the number of emitted electrons is smaller than normal so that deconcentration occurs. The average electronic stream is not contributive to the alternating anode current so that it may be left out of consideration. Hence, the alternating anode current may be conceived to result from positive and negative charges alternately passing through the electrode preceding the anode, which charges travel to the anode where they are neutralized.

In Figures 3 and 4 two possible cases are illustrated diagrammatically. In these figures are diagrammatically represented an anode 4 and a screen grid 1. In accordance with what has been said above, the succeeding concentrations and deconcentrations of the electronic stream are represented by positive and negative charges which are schematically represented by bullets alternately bearing a plus and a minus sign. For the sake of simplicity we will first consider the case in which the anode and screen grid have the same potential so that the electrons travel at a constant speed from the screen grid to the anode and consequently the anode current is proportional to the total charge of the electrons staying between the two said electrodes.

Figure 3 shows the case in which the transit time of the electrons from the screen grid to the anode amounts to an even number of times the period of the oscillations to be amplified. In this case the number of concentrations on the way is always as large as the number of deconcentrations, in other words there are always as many positive as negative bullets on the way from the screen grid to the anode. Consequently the total charge on the way is constant, so that the alternating anode current is equal to zero. Hence, with this relation between the transit time and the period the effective mutual conductance equals zero.

Figure 4 shows the case in which the transit time of the-electrons is an .odd multiple of the half cycle of the oscillations to be amplified. In this case all bullets but for one will neutralize each other as regards the influence on the alternating anode current, as is schematically indicated by a dotted framing in the figure. However, the last bullet will alternately be positive and negative so that it will produce an alternating anode current. This bullet, however, is active only during a small part of its transit time andmore particularly for an nth part, if the transit time amounts to n half cycles. Upon calculation it is found that in this case the effective mutual conductance amounts to vrn times the static mutual conductance.

In Figure 5 the effective mutual conductance is graphically represented as a function of the product wt, in which 0.: represents the angular frequency of the oscillations to be amplified and t the transit time of the electrons from the electrode preceding the anode to the anode. The curve I applies for the above mentioned case in which the electrons travel at a constant speed through the space between the two said electrodes. As appears from this curve the mutual conductance equals zero if cut is an even multiple of 1r, whereas the mutual conductance is equal to times the static mutual conductance at the points at which mi is an odd 72-fold of 1r.

When the anode and the preceding electrode are at difierent potentials, so that the speed of the electrons between these electrodes is variable, the succeeding bullets in Figures 3 and 4 will have different speeds so that in regard to their action exerted on the alternating anode current they can no longer neutralize each other completely. In this case the curve of the mutual conductance will be slightly less steep. In Figure 5 the curve II applies for the extreme case in which one of the two electrodes in question is at zero potential so that the electrons enter the said space or leave it at zero speed respectively. The mutual conductance occurring in practice will always lie in the area enclosed by the two curves I and II.

The invention consists in preventing mutual neutralization of the succeeding bullets by taking care that there always is at the most one bullet in the space between the anode and the preceding electrode. Consequently, in front of the output electrode there must always be an electrode which is connected to the end of the output impedance remote from the output electrode and whose distance from the output electrode is covered by the electrons in less than half a period of the oscillations to be amplified. By complying with this condition it can be achieved, as may be read from the curves shown in Figure 5, that the effective mutual conductance amounts at least to 6,5 to 75% of the static mutual conductance.

A simple rule with which the distance between the output electrode and the preceding electrode must comply can be deduced as follows. As is well known the speed of an electron is equal to DEBXIUZVE where '0 represents the speed expressed in cm./sec. and u the traversed potential expressed in volts. When defining an average potential uav by the relation 17av=6X10 Vuav, in which Dav represents the mean speed of the electrons between the output electrode and preceding electrode then, according to the invention, the relation A a 6X lOH/u X cr m/17;?

expressing a in mm. and A in m. We. have In the above considerations we assumed that an electrode cannot affect electrons at the other side of the preceding electrode, in other words the field of the preceding electrode. was neglected. When neglect thereof is not admissible the fact has to be taken into account that the current of the output electrode is also determined by electrons at the side of the preceding electrode remote from the output electrode. In practice the field of preceding electrodes through the next adjacent electrode in modern tubes is always negligible except at the suppressor grid of a pentode. In fact this last mentioned electrode usually has such wide meshes that the field of the anode volt age extends through the suppressor? grid. Con sequentl in pentodes and similar tubes the anode current is also determined by the electrons in the space between the screen grid and the sup ressor grid. In conjunction therewith it is in general not the distance from the anode-to the suppressor grid but the distance from the anode to the screen grid which is decisive for the effective mutual conductance in tubes of this kind. Consequently, whenever the distance between the node and the preceding electrode is concerned hereinbefore it is necessary in pentodes and similar tubes to con--. sider the distance between the anode and the screen grid.

The use of the invention is of particular importance in cases in which a much greater mutual conductance than that of a miniature tube is required. This is why according to the inven-v tion use is preferably made of an amplifying tube whose mutual conductance exceeds 3 ma./v. Generally one or more of the above exped-ients for reducing the input damping and, if desired, also the. output damping will have to be taken at the same time.

The invention will be more fully explained by reference tothefollowing examples.

Hence we In the well known pentodes the.

tance between the anode and the, screen grid If, for instance, the.

amounts to about 4 mms. anode voltage amounts to 250, voll and the screen grid voltage to.100 volts then Vuat will approxisequently, in accordance with the formula deduced above the known tubes can be used with the said operating voltages to a wavelength of of less than 1 m., the distance between the anode and the screen grid being smaller than 3 mms. and the suppressor grid being preferably shaped as a window.

The minimum distance between two electrodes, which may be deemed possible at the present state of the art amounts to about 0.8; mm. By means of a screen grid tube, in which the distance between the anode and the screen grid is. 0.8 mm. sufficient amplification at the above value of the operating voltages would be possible to a minimum wavelength of about 6 cms. At higher operating voltages suflicient amplification of even shorter waves will be possible.

In secondary emission tubes the distance between two succeeding secondary. emission electrodes and between the last secondary emission electrode and the anode respectively always amounts at least to 15 mms. forelectro-optical reasons. The voltage between two succeeding secondary emission electrodes and between the last secondary emission electrodes and the anode usually amounts to about 1 00. volts. When taking into account that the secondary electrons leave the s econdary emission electrodes at zero speed /uav may be assumed to be about /2 /=5, so that hitherto a secondary emission tube did not permit sufiicient amplification at a wavelength shorter than Since the distance between two succeeding secondary emission electrodes and between the last secondary emission electrode and the anode respectively cannot bereduced a -scr-een is, according to the invention, placed in front of the anode at a distance covered by the secondary electrons in less than half a period, which screen is connected to the end of the output impedance remote from the anode so that it will generally be earthed for high frequencies. possible to provide such a secondary emission tube that will amplify wavelengths below 3 m., for instance to a minimum wavelength of 10 cms. To the said .screen is applied a positive bias with respect to the last secondary emission electrode. In a circuit including .a secondary emission tube which comprises onesecondar-y emission electrode it is known, to connect the, output impedance between the anodev and the secondary emission; electrode and to connect theccnter ottheoutput In this way itis 9 impedance to the cathode. In this case the sec ondary emission electrode acts as an output electrode at the same time.

Such a circuit is also possible for very short waves when, according to the invention, a screen connected for high frequencies to the cathode is provided in front of the secondary emission electrode acting as an output electrode at a distance covered by the electrons in less than half a period of the oscillations to be amplified. Since the stream of secondary electrons is much stronger than the stream of primary electrons impinging on the secondary emission electrode the said screen, if possible, is not located in the path of the primary electrons, but exclusively in the path of the secondary electrons. In this case it is advantageous to give the distance between the secondary emission electrode and the preceding electrode such a value that the primary alternating current flowing in the circuit of the secondary emission electrode is as small as possible, since this primary alternating current is in phase opposition in regard to the secondary current so that it will only reduce the total current of the secondary emission electrode. Independently of the intensity of the primary current flowing in the external circuit of the secondary emission electrode the secondary electrons are dislodged by the primary electrons impinging under all conditions on the secondary emission electrode, so that by a suitable choice of the electrode distances a decrease of the external primary current does not involve a decrease of the secondary current.

If the wavelength of the oscillations to be amplified is not too short it will be suflicient to place one screen between the secondary emission electrode and the anode. At shorter wavelengths two screen-s must be provided. These two constructions are represented in Figures 6 and '7.

Figure 6 shows a circuit according to the invention including a secondary emission tube 8 which comprises a cathode 9, a control grid l0, 9, screen grid H, a secondary emission electrode I2 and an anode l3. Between the control grid l and the cathode 9 is provided an input circuit l4, and an output circuit l whose electric center I6 is earthed is connected in push-pull arrangement between the anode l3 and the secondary emission electrode 12. Between the two last mentioned electrodes an additional screen grid I 1,

which is earthed for high frequencies and by which the space between the anode and the secondary emission electrode is divided into two parts, each of which is covered by the secondary electrons in less than half a period of the oscillations to be amplified, is provided in the path of the secondary electrons. The output impedance (5 consists of two parts of which the upper part lies between the anode and the screen l1, whereas the bottom part is located between the screen grid l1 and the secondary emission electrode. Consequently, both parts of the output impedance are connected between two electrodes which are placed in the path of the electrons and whose distance is covered by electrons in less than half a period.

It is to be noted that the proposed push-pull connection of the output impedance between the anode and the secondary emission electrode is only efiective when the phase displacement between the anode current and the current from the secondary emission electrode lies between 90 and 270. In the case of phase displacements between -90 and +90 the two said electrodes 10 must be connected in parallel to the output impedance.

The last mentioned circuit is represented in Figure '7 which also illustrates the case in which the distance between the secondary emission electrode and the anode has such a value that it can no longer be divided by one screen into two parts each of which is covered by the electrons in less than half a period. For this reason two screens I1 and I8, which are earthed for high frequencies, are provided between the anode and the secondary emission electrode; both of these screens are placed in the path of the secondary electrons, the screen I1 being located at the prescribed distance from the anode, and the screen l8 being placed at the prescribed distance from the secondary emission electrode.

For the sake of simplicity the direct current connections are omitted in Figures 6 and 7. However, it will be obvious that a negative bias must be applied to the control grid l0, whereas the electrodes H, 12, I3, I! and, if required, l8 must be positively biased.

The distance between the screen grid H and the secondary emission electrode I2 is preferably so chosen that the primary current in the external circuit of the secondary emission electrode is as small as possible.

In the electron multiplier comprising two or more secondary emission electrodes a plurality of secondary emission electrodes may contribute to the output current. In this case a, screen earthed for high frequencies must be provided for each secondary emission electrode acting as an output electrode, said screen being placed in the path of the secondary electrons issuing from the electrode in question at a distance which is covered by the secondary electrons in less than half a period of the oscillations to be amplified. For earthing these screens use is preferably made of a Lecher wire system, wherein the screens and, if required, the secondary emission electrodes not acting as an output electrode are connected to voltage nodes of the systems, whereas the output electrodes are connected between the voltage nodes at suitable points. i

In all cases referred to above it is of importance to provide by suitable expedients, for instance by electric or magnetic focusing means, that the transit time of all electrons should be the same. In fact, when two electrons issued at the same time arrive with a time difference corresponding to half a period they will exactly neutralize each other. More particularly in electron multipliers these differences in transit time may become so large as to give rise to a considerable loss of mutual conductance,

While we have indicated the preferred embodiments of our invention of which we are now aware and have also indicated only one specific application for which our invention may be employed, it will be apparent that our invention is-by no means limited'to the exact forms illustrated or the use indicated, but that many variations may be made in the particular structure used and the purpose for which it is employed without departing from the scope of our invention as set forth in the appended claims.

What we claim as new is:

1. An electron discharge device for use at ultra high frequencies having a cathode, a control electrode, a screen electrode and an anode, an input circuit for applying a voltage of a predetermined. frequency to said control electrode, the transit time of the electrons from said cathode to said anode being greater :than the period'of oscillation of the applied voltage, an output circuit'connected'atone end to-said anode, said screen elec- 'trolde and'anode-being spaceda-distance less than the "distancetraveled by-an electron during one- J half-the period of oscillation oftheapplied control voltage, and a-connection' between the screen electrode andsaid'output-circuit at a point-re- -moved fromtheconnection to said: anode.

,2. 'An' electron discharge device for use at ultra "high'frequencieshavinga cathode, a control electrode, a screen electrode and-an anode in the order named, an input circuit for applying a voltage of a;predeterminedfrequency-to said control electrode, the transit" time'of the-electrons from 'said cathode to=said-anodebeing greater than the period of oscillation-of theapplied voltage, an output circuit conneeted'at'one end to said anode, ,said screenelectrodeandanode being spaced a distance less than the "distance traveled by an :electron gduring one-half the period of oscillation of the applied control voltage, and a connection between the screen-electrode and said output circuit *at the otherend=of the output circuit-from said anode.

-3. Anelectron discharge devicefor-useatultra high frequen'cies-havinga cathode,-a control grid,

a screen grid and an anode, an input circuitfor applying a=voltage of a predetermined frequency to said control grid, the' transit time -o'fi-the' electrons from said cathode to said anode :being greater thantheperiod of oscillation eithe /applied voltage, --an output circuit connected-at one end "to said anode, said screengrid and anode being spaced a distance less *than the distance traveled by an electron during :out-half the 'pe- 'riod of oscillation of the applied control "voltage, andaconnectionbetween thescreengridand'said output circuit at a point removedfromthe connection to'said-anode.

'4. An electron discharge device for useat'ultra high frequencieshavin'g a cathode, a control electrode, a screen --electrode and an anode in "the order named, an input circuitforepplyinga voltage of :a predetermined 'frequencyto said =control electrode, the transit time of the-electronsirom saidcathode to sa'idanode 'being greaterzthan the period of oscillation of the applied voltage, an output circuitconnected atone end to=said:anode, said screen electrode an'danodebeing spaced a distance in millimeters less than IO- M/uav, where i=wavelength of applied woltage and uav=average potentialof'volts'btweenthe screen electrode and anode, and -a-connection between the screen-electrode and-said load circuit 'at a point removed-'from the connection to said anode.

5. An electron dischargedevice havinga cathode, 'a control electrode, a screen electrode and ananode, and a secondaryemitting electrode po- "sitioned between the control electrode and the 60 screen 'electrode, -a circuit for applying voltage "of a predetermined frequency to 'said control electrode. and an output circuithaving one end :connected to saidanode, the'spacing'between said screen electrode and *said'anode being'less than trode, and;an:.output circultfhavingmne-end connected to said anode, thesspacingahetweemsaid screen electrode and secondaryemitting electrode and 1 said xscreen "electrode 2 and saidanode being less than thezdistance: thatsan-zelectron travels in one-half the :period :ofxoscillation of'ithe applied control voltage.

:7. An electron-discharge::device: having a cathode; a control-electrodepa screen electrode and an .anode,: and acsecondaryemitting electrode positioned between ithe "control electrode and i the :screen electrode, ia second screen-electrode i be- ;tween:saidsecondaryemitting-electrode and con- :trolelectrode, azcircuit: for applying voltage of a :predetermined Ffrequency to :said control a-elec- :trode, and rantoutputicircuit' having one end con- "nected 'to said'zanode, ,the spacingwbetweenthe rfirstscreen electrode and,,-said anode-being less than the distance ,t-hat an -;electron travels in one-halftheaperiod" of oscillation, of: the applied control voltage.

558. An :electron' :dischargel-device: havingra cath 'rode, a: control electrode gascreenelectrode and an ,:anojde;and a secondaryemitting-electrode posiitioned between the ;,control ':816Ci710d6 and the :screen electrode,. ;a-:circuitfor: applying voltage of a1 predeterminedfrequency" to. said control electrode,- andwanoutput'circuithaving one end connected to said-:a-node, :the spacing 1 between said i-screen: electrode ;and saidranode being less than the distance that an electrontravels in one-half the period of oscillation -,of A the. applied control voltage,- an electricalconnection between said sec- .ondary emitting electrode ande-a ,point on .said

5 ,load circuit. removed from-the anode connection ,and ,another electrical connection 'between the screen and an .rintermediate point i on said load circuit.

9. ,An electron 1, dischargeedevice havinga cath- Jm ,ode. a control velectrode, 2 8, screen electrode and an anode, ,and .a -secondary remitting electrode 7 positionedibetween the ,controlelectrode and the screen electrode, .a second screen electrode between said c0ntrol, grid ..and saidlsecondaryflemittitle electrode,.a.,third screen electrode between of oscillation, of the applied control voltage.

MAXIMILIAAN JULIUS ,OTTO STRUII'. ALDERT VAN mm ZIEL.

REFERENCES CITED The n references .are.of record'in1th filel of ,this patent: v

STATES'EPKTENTS Number ;Name Date 2,I6'7-,201 "Dallenbach J.uly25, 1939 2,314,794 Linder 'Mar.'23, 1943 2,305,395 Strutt et al. ..,Dec.15,1942 --2,'314,916 Alma et'al. ..-Mar.'30, 1943 ,EOBEIGN .BATENTS ;Number :Country Date 115,023 .nustralia r Qct. 11,1940 525,951 Great Britain :Septii, 1940 

